Effect of Isolated Vertical Fractures Existing in the Reservoir On Fluid Displacement Response

1966 ◽  
Vol 6 (01) ◽  
pp. 81-86 ◽  
Author(s):  
J.W. Givens ◽  
Paul B. Crawford
Keyword(s):  
Gas Injection ◽  
Great Influence ◽  
Dimensionless Time ◽  
Spot Pattern ◽  
Sweep Efficiency ◽  
Copper Strip ◽  
Vertical Fracture ◽  
Fluid Displacement ◽  
The Matrix ◽  
Vertical Fractures

Abstract A potentiometric model study has been made of the effect of vertical fractures existing in the matrix of the reservoir on the flooding or cycling performance. Fractures can have unusual flow characteristics. Fluid entering one side of a fracture can emerge on either the same or opposite side of the fracture, depending on the particular streamline. Fracture orientation has a great influence on the sweep efficiency. However, sustained fluid injection may still permit large areas to be swept. Introduction One can find considerable information available in the literature on the effect of fractures originating at the wellbore on sweep efficiencies of waterflooding or gas cycling programs. However, there are few, if any, quantitative data reported in the literature on the effect of vertical or horizontal fractures existing out in the reservoir matrix on secondary recovery performance. Several papers have been presented on the effect of vertical and horizontal fractures on the productivity or conductivity of waterflood and gas injection patterns, but in all cases the fractures initiated at the well and simulated commercial fractures. It is believed that natural fractures may exist out in the reservoir matrix and would effect the displacement performance. The purpose of this report was to study the effect of a few isolated vertical fractures existing out in the reservoir matrix on the performance of waterflood or gas injection patterns. DESCRIPTION AND EQUIPMENT Since the potentiometric model was described by Lee it has been widely used to study numerous types of fluid displacement problems. The potentiometric model can be used for fluid displacement studies when the following assumptions are valid:(a) steady-state conditions exist;(b) the mobility ratio is one; and(c) the capillary and gravitational effects can be neglected. Five-spot and direct line drive square patterns were studied using a copper strip of the desired length and orientation to simulate a vertical fracture in the reservoir matrix. The 20 x 20-in. model was considered to represent only one element of an infinite array of similar patterns. DISCUSSION AND RESULTS FIVE-SPOT PATTERN ONE FRACTURE BETWEEN INJECTION AND PRODUCING WELLS Fig. 1 shows a quadrant of a five-spot pattern with the vertical fracture existing out in the matrix along a line connecting the injection and producing wells. Length of the fracture was equal to 35.4 per cent of the distance between injection and producing wells. In this particular pattern it is noted that fluid breaks through from the injection well to the producing well when the dimensionless time is equivalent to 26.9. Dimensionless time is defined as volume of fluid injected divided by the volume of displaceable fluid in the pattern expressed as a per cent. SPEJ P. 81ˆ

The Effect of Induced Vertically-Oriented Fractures on Five-Spot Sweep Efficiency

1968 ◽  
Vol 8 (03) ◽  
pp. 260-268 ◽  
Author(s):  
D.A.T. Donohue ◽  
J.T. Hansford
Keyword(s):  
Production Capacity ◽  
Theoretical Work ◽  
Fracture Pattern ◽  
Flow In Porous Media ◽  
Fracture System ◽  
Sweep Efficiency ◽  
Compass Direction ◽  
Vertical Fracture ◽  
Fluid Displacement ◽  
Vertical Fractures

Abstract Substantial evidence indicates that many petroleum producing horizons contain naturally occurring, ordered fracture systems and that within a particular geologic zone, vertical fractures induced in wellbores often will be directed along a particular compass direction. Both conditions will seriously alter the fluid displacement behavior within reservoirs. In this study the effect of induced fracture orientation and length on sweep efficiency is determined for a five-spot pattern. In general, it is assumed that all wells are fractured and directed along the same compass direction. Using the electrical analog to steady state, two-dimensional fluid flow in porous media, boundary conditions are obtained from which flood fronts are tracked numerically. The numerical computations require a particle tracking routine for approximating flood front histories. It is shown that recovery is sensitive to the length and orientation of fractures for the pattern studied. With the proper design of fracture-pattern systems, recovery can be enhanced considerably. Introduction Hydraulic fracturing introduced in 1949, gave the industry a rather inexpensive means of increasing the fluid injection or production capacity of wells. It has been used with particular success to increase the production rate of wells completed in tight formations, such as in western Pennsylvania where producers have fractured in depleted or near-depleted fields and observed economic responses. Once the natural energy declines in such a reservoir where all wells have been fractured, waterflooding is generally suggested as means of further increasing recovery. Of the dual objective sought in waterflooding -- high injectivity and high break-through sweep efficiency - the former condition can be obtained if all wells in the flood pattern are fractured; the latter condition should depend on the nature of the fracture system. Considerable theoretical work has been published on the nature of fractures induced in boreholes. Although discussion persists concerning the possibility of forming a horizontal at a given point within the wellbore, it is generally conceded that only vertical fractures will develop below a given depth, i.e., where the fracturing pressure is less than the overburden load. Given the fact that fractures will be vertical in most cases of interest, it is also important to know whether there is order to fracture orientations within a given geological region. Kehle has suggested that in tectonically relaxed areas of uncomplicated geology, the stresses are fairly uniform and all fractures in the region should be parallel. Dunlap arrived at a similar conclusion in a theoretical investigation of localized stress conditions surrounding the borehole. He concluded that most vertical fractures are propagated in a preferred azimuthal direction. Fraser and Pettitt, in extending these theoretical suggestions to a specific field case, used an impression packer to record both a vertical fracture and the orientation of this fracture in the wellbore of a well in the Howard Glasscock field, Tex. Use of this information enhanced the waterflood recovery of the field. Anderson and Stahl also used impression packers on three fractured wells in the Allegheny field, N. Y., and found that the fractures were oriented more or less along the same compass direction. Orientation of the fractures in this manner depends on the stress condition within the formation during fracturing. Elkins and Skov have demonstrated that a natural, oriented, vertical fracture system exists within the Spraberry field. SPEJ P. 260ˆ

The Water Absorption Rule of Vertical Fractured Well

2014 ◽  
Vol 624 ◽  
pp. 573-576
Author(s):  
Zhong Guo Wang ◽  
Guang Yu Zhang ◽  
De Kai Zhou ◽  
Yi Qing Li ◽  
Wen Ping Song
Keyword(s):  
Raw Materials ◽  
Water Injection ◽  
Uniform Flow ◽  
Injection Wells ◽  
Vertical Fracture ◽  
Flow Formation ◽  
Key Factor ◽  
Fractured Well ◽  
Bottomhole Pressure ◽  
Vertical Fractures

Oil is an important energy and chemical raw materials and strategic materials. Nowadays, the layered water injection test technology become the key factor of oilfield production. According to different types of formation and for the artificial fracturing injection wells, this paper studied the infinite boundary, uniform flow and vertical cracks well, infinite diversion vertical fractures and conductivity vertical fracture wells’ absorbent law. The method to do all of the above work is to solve the equation of dimensionless bottomhole pressure in different formation and boundary conditions. The indicating curve of infinite uniform flow formation, unlimited conduction and limited conduction vertical fractures wells are almost identical, which means that the type of vertical fracture has little effect on the indicate curves of injection wells.

A Feasibility Study of an In Situ Retorting Process for Oil Shale

1968 ◽  
Vol 8 (03) ◽  
pp. 231-240 ◽  
Author(s):  
Allen L. Barnes ◽  
Allen M. Rowe
Keyword(s):  
Heat Transfer ◽  
Oil Shale ◽  
Gas Injection ◽  
Thermal Capacity ◽  
Order Partial Differential Equation ◽  
Conduction Heat Transfer ◽  
Hot Gas ◽  
Transfer Study ◽  
Vertical Fractures

Abstract A heat transfer study was made of hot gas injection into oil shale through wells interconnected by vertical fractures. This analysis involved the simultaneous numerical solution of a nonlinear, second-order partial differential equation that describes two-dimensional conduction heat transfer in oil shale and a non linear first-order partial differential equation that describes convection heat transfer in the fractures. Three nonlinear, temperature-dependent coefficients were used in this work; they are thermal conductivity, thermal capacity and retorting endothermic heat losses of oil shale. Vertical fractures were considered to be of finite height. Although vertical conduction heat transfer was not considered, an estimate of the error resulting from this limitation was made. How retorting efficiency was affected by injected gas temperature, injection rate, system geometry, cyclic injection and time were investigated. Results from this study show that the rate of retorting oil shale is a direct function of both injection temperature and rate, and the theoretical producing air-oil ratio:(AOR) is an inverse function of temperature. Retorting rates are constant until "breakthrough" of the 700 F isotherm at the producing. well, assuming constant injection parameters. Retorting rates for bounded systems are higher than the analogous unbounded systems and likewise AOR's are less. The use of an alternating injection-soak routine with high injection rates is less efficient than continuous injection at lower rates. These results indicate that injection temperatures on the order of 2000 F or greater may give theoretical AOR's in the economic range. Introduction Over half of the known oil shale reserves are located in the U.S., and most of them lie in the Piceance Creek basin of Western Colorado. The Colorado oil shale outcrops on the edges of the Piceance Greek Basin. At the outcrops the shale beds are relatively thin, from 25 to 50 ft thick. In the center of the basin the oil shale is as great as 2,000 ft thick and is covered with 1,000 ft of overburden. It has been estimated that there are over 1,000 billion bbl of oil in shales having an oil content over 15 gal/ton in this basin. Oil shale does not contain free oil but an organic matter called kerogen. Kerogen yields petroleum hydrocarbons by destructive distillation. It must be heated to approximately 700 F, at which temperature it decomposes into shale oil, gases and coke. The U.S. Bureau of Mines and, more recently, oil companies have conducted considerable research on surface retorting methods to economically recover oil from this shale. Another approach to exploit the oil shale deposits, in particular that portion having 1,000 ft of overburden, is to retort the oil shale in place and produce the liquid and gaseous hydrocarbons through wells drilled into the shale. Some research has been done on this approach. There are several variations to the in situ retorting approach. These variations fall into one of two groups, depending upon the geometry of the system:retorting in a highly fractured or broken up matrix;retorting from single fractures between production and injection wells. The latter is the group studied. Several investigators, using various assumptions, have studied flow of heat through horizontal systems. The objective of this work was to make a heat transfer study of in situ retorting oil shale by hot gas injection through wells interconnected by single vertical fractures of finite height. The oil shale thermal conductivity, thermal capacity and retorting endothermic heat losses were considered to be functions of temperature. SPEJ P. 231ˆ

scholarly journals Characteristics and quantitative study on gas breakthrough in developing Yaha-2 condensate gas reservoir in Tarim Basin, China

2018 ◽  
Vol 36 (4) ◽  
pp. 787-800
Author(s):  
Jing Xia ◽  
Pengcheng Liu ◽  
Yuwei Jiao ◽  
Mingda Dong ◽  
Jing Zhang ◽  
...  
Keyword(s):  
Tarim Basin ◽  
Prediction Models ◽  
Graphical Representation ◽  
Gas Injection ◽  
Dew Point ◽  
Breakthrough Time ◽  
Sweep Efficiency ◽  
Reservoir Properties ◽  
Gas Reservoir ◽  
Point Pressure

In order to keep the formation pressure be larger than the dew-point pressure to decrease the loss of condensate oil, cyclic gas injection has been widely applied to develop condensate gas reservoir. However, because the heterogeneity and the density difference between gas and liquid are significant, gas breakthrough appears during cyclic gas injection, which apparently impacts the development effects. The gas breakthrough characteristics are affected by many factors, such as geological features, gas reservoir properties, fluid properties, perforation relations between injectors and producers, and operation parameters. In order to clearly understand the gas breakthrough characteristics and the sensitivity to the parameters, Yaha-2 condensate gas reservoir in Tarim Basin was taken as an example. First, the gas breakthrough characteristic of different perforation relations by injecting natural gas was studied, and the optimal relation was achieved by comparing the sweep efficiency. Then, the designs of orthogonal experiments method were employed to study the sensitivity of gas breakthrough to different parameters. Meanwhile, the characteristic parameters, such as gas breakthrough time, dimensionless gas breakthrough time, and sweep volume, were calculated and the prediction models were achieved. Finally, the prediction models were applied to calculate the gas breakthrough time and sweep volume in Yaha-2 condensate gas reservoir in Tarim Basin. The reliability of the model was verified at the same time. Please see the Appendix for the graphical representation of the abstract.

scholarly journals Two-dimensional numerical investigations on the termination of bilinear flow in fractures

2013 ◽  
Vol 5 (1) ◽  
pp. 391-425
Author(s):  
◽  
R. Jung ◽  
J. Renner
Keyword(s):  
Flow Field ◽  
Master Curve ◽  
Radial Flow ◽  
Dimensionless Time ◽  
Linear Flow ◽  
Type Curves ◽  
Straight Line ◽  
The Matrix ◽  
Line Characteristic ◽  
Fourth Root

Abstract. Bilinear flow occurs when fluid is drained from a permeable matrix by producing it through an enclosed fracture of finite conductivity intersecting a well along its axis. The terminology reflects the combination of two approximately linear flow regimes, one in the matrix with flow essentially perpendicular to the fracture and one along the fracture itself associated with the non-negligible pressure drop in it. We investigated the characteristics, in particular the termination, of bilinear flow by numerical modeling allowing an examination of the entire flow field without prescribing the flow geometry in the matrix. Fracture storage capacity was neglected relying on previous findings that bilinear flow is associated with a quasi-steady flow in the fracture. Numerical results were generalized by dimensionless presentation. Definition of a dimensionless time that other than in previous approaches does not use geometrical parameters of the fracture permitted identifying the dimensionless well pressure for the infinitely long fracture as the master curve for type curves of all fractures with finite length from the beginning of bilinear flow up to fully developed radial flow. In log-log-scale the master curve's logarithmic derivative initially follows a 1/4-slope-straight line (characteristic for bilinear flow) and gradually bends into a horizontal line (characteristic for radial flow) for long times. During the bilinear flow period, isobars normalized to well pressure propagate with fourth and second root of time in fracture and matrix, respectively. The width-to-length ratio of the pressure field increases proportional to the fourth root of time during the bilinear period and starts to deviate from this relation close to the deviation of well pressure and its derivative from their fourth-root-of-time relations. At this time, isobars are already significantly inclined with respect to the fracture. The type curves of finite fractures all deviate counterclockwise from the master curve instead of clockwise or counterclockwise from the 1/4-slope-straight line as previously proposed. The counterclockwise deviation from the master curve was identified as the arrival of a normalized isobar reflected at the fracture tip sixteen times earlier. Nevertheless, two distinct regimes were found regarding pressure at the fracture tip when bilinear flow ends. For dimensionless fracture conductivities TD < 1, a significant pressure increase is not observed at the fracture tip until bilinear flow is succeeded by radial flow at a fixed dimensionless time. For TD > 10, the pressure at the fracture tip has reached substantial fractions of the associated change in well pressure when the flow field transforms towards intermittent formation linear flow at times that scale inversely with the fourth power of dimensionless fracture conductivity. Our results suggest that semi-log plots of normalized well pressure provide a means for the determination of hydraulic parameters of fracture and matrix after shorter test duration than for conventional analysis.

scholarly journals Prediction of Wellbore Temperatures During the Scientific Ultra-Deep Drilling Process

2015 ◽  
Vol 8 (1) ◽  
pp. 451-456 ◽  
Author(s):  
Fanhe Meng ◽  
Aiguo Yao ◽  
Shuwei Dong
Keyword(s):  
Drilling Fluid ◽  
Great Influence ◽  
Inlet Temperature ◽  
Drilling Process ◽  
Fluid Viscosity ◽  
Key Factors ◽  
Deep Drilling ◽  
Fluid Displacement ◽  
Temperature Distributions ◽  
Wellbore Temperature

In order to carry out a series of key basic researches, a scientific ultra-deep drilling plan is being undertaken in China. Wellbore temperature is one of the key factors during the drilling process. In this paper, we established a twodimensional transient numerical model to predict the ultra-deep wellbore temperature distributions during circulation and shut-in stages. The simulation results indicate that the cooling effect of drilling fluid circulation is very obvious, especially during the inception phase. Drilling fluid viscosity has great influence on the temperature distributions during circulation stage: the lower the viscosity, the higher the bottomhole temperature. While drilling fluid displacement and inlet temperature have a little effect on the bottomhole temperature. During the shut-in stage, the wellbore temperature recovery is a slow process.

scholarly journals Numerical modeling of molecular diffusion and convection effects during gas injection into naturally fractured oil reservoirs

2021 ◽  
Vol 76 ◽  
pp. 81
Author(s):  
Hossein Gholamian ◽  
Mohammad Reza Ehsani ◽  
Mohammad Nikookar ◽  
Amir H. Mohammadi
Keyword(s):  
Molecular Diffusion ◽  
Gas Injection ◽  
Laboratory Data ◽  
Nitrogen Injection ◽  
Matrix Block ◽  
Naturally Fractured ◽  
The Matrix ◽  
Diffusion And Convection ◽  
Initial Recovery ◽  
The Mathematical Model

Gas injection into a naturally fractured oil reservoir keeps the reservoir pressure and increments the initial recovery from the reservoir. The main aim of this work was to develop a numerical model to calculate the mass transfer (molecular diffusion and convection) between a gas injected in the fracture and residual fluid (gas and oil) in a matrix block. The dual continuum model is applied to describe flow behaviour and fluid recovery in porous media. Finally, the model is validated by comparing the outcomes with the results of two experimental works available in the literature. The mathematical model results are in agreement with the laboratory data including recovery of each component, saturation profile, and the pressure gradient between matrix and fracture. Modeling results show that after 25 days of N2 injection, the lighter and heavier components (C1 and C5) are recovered about 51% and 39%, respectively. These amounts for CO2 injection are 49% and 27%. It is found that the convection mechanism has a great effect on preventing the pressure drop of the reservoir during injection operations. In the nitrogen injection, without considering the convection, after 30 days, the matrix pressure reaches 1320 Psi from 1479 Psi but after 30 days, considering the convection, the pressure reaches 1473 Psi from 1479 Psi.

scholarly journals Experimental Study on Gas Breakthrough Prevention by Flue Gas Drive

2020 ◽  
Vol 218 ◽  
pp. 02022
Author(s):  
Ping Guo ◽  
Shiyong Hu ◽  
Yisheng Hu ◽  
Qijian Ding
Keyword(s):  
Flue Gas ◽  
Gas Injection ◽  
Low Permeability ◽  
High Permeability ◽  
Sweep Efficiency ◽  
Water Alternating Gas ◽  
Vertical Heterogeneity ◽  
Profile Control ◽  
Gas Flooding ◽  
Gas Drive

The heterogeneity of glutenite reservoir is serious, and breakthrough is easy to occur in the process of water drive and gas drive, which reduces the sweep efficiency. The serious vertical heterogeneity in the H well area of Xinjiang oilfield led to the rapid gas breakthrough during gas injection test. Water alternating gas flooding and foam profile control are often used to seal breakthrough. In this paper, based on the actual reservoir characteristics, vertical heterogeneous planar model is made for flooding experiment. The experimental results show that after gas breakthrough caused by water alternating gas flooding, the flue gas foam can effectively block the high permeability layer and develop the low permeability layer, improve the sweep efficiency and recovery percent, and provide reference for the development adjustment of actual reservoir after gas breakthrough.

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